The application of dental restorations to the teeth of patients requires the use of specially formulated dental adhesives that will be effective to form a bond with a surface of the patient's dental anatomy. The more effective of the adhesives currently having the most widespread use include resins that are applied to a tooth surface, for example, and then cured with ultraviolet or visible light. With certain formulations of such light cure adhesives, a small amount of such light is sufficient to start an adhesive curing reaction that will propagate through the entire dose of adhesive. Other types of adhesives require larger exposures to such light for the cure of the entire body of the adhesive. Such adhesives are used for the bonding of more transparent or semi-transparent restorations, such as direct restorations, veneers and other thin, small or in situ formed composite restorations.
The more effective of the dental adhesives for the uses discussed above have been provided to dentists in multiple parts. The various parts of these multi-part adhesive systems take advantage of the different properties at different parts of the system at the different stages of their use. A first part of the system may include, for example a primer, which is painted onto an area of the tooth to which the restoration is to be attached. The primer dries the surface and penetrates to form a basis for an effective bond. A second part may include a filled or an unfilled resin that is applied over the first part to interact with it and form a bond. In some forms, the second part is itself supplied in two parts. In a superior form a subpart of the second part is a resin and the other subpart is a fill material in the form of minute glass beads. The fill, which is mixed to a content of about 48% of the mixture with the resin, contributes strength and shock absorbency to the bond. Multi-part adhesives of this type are available in an alcohol base and marketed under the trademarks Optibond and Optibond FL by Kerr Dental Materials Center of Orange, Calif.
The application of each part of the multi-part adhesive system by a dentist calls for the coating of a small area of a patient's tooth, for example, with a small quantity of each part of the adhesive system being applied. The coating with each adhesive part is followed by the placement of the restoration, which may be a restoration formed in a dental laboratory on a model of the patient's teeth that is transferred by the dentist onto the patient's dental anatomy or may be a restoration formed in situ by the dentist, usually from a composite material. The different parts of the multi-part adhesive systems are traditionally packaged in containers designed to hold a quantity of material sufficient for bonding multiple restorations and which can be resealed after each use. In a one part adhesive, a single container designed to hold a quantity of material sufficient for bonding multiple restorations in the treatment of multiple patients and which can be resealed after each use is used. To use such containers, the dentist or dental assistant is required to retrieve the containers for each part of the adhesive system from a storage area, open each container, dispense from each container into another container (typically a container which constitutes an open well) the required amount of the adhesive part being dispensed, reseal each container for each adhesive part and return the containers to the storage area.
If the adhesive system being used has multiple second parts, the different parts are generally dispensed into the same container well and mixed before application to the tooth. If the system is a one part adhesive, only one container must be opened.
After the adhesive parts have been applied to the tooth, the containers into which the adhesive parts were dispensed is generally disposed of.
The handling and use of multiple part adhesives is regarded by many dentists as inconvenient. With direct restorations particularly, the need to handle and mix separate parts of the adhesive is an inconvenience, in part because the composite material of which the restoration is formed also must be handled and mixed. While one part or premixed adhesives are available, such adhesives do not include fills or fluoride release and many are formulated with an acetone base. Acetone based adhesives tend to degrade after being opened as their solvent components tend to evaporate, altering the adhesive composition, and are regarded as less desirable by many dentists or patients.
One such acetone based adhesive is a one part adhesive comprised predominantly of an acetone solvent and a Penta-P adhesion promoter. The composition contains no fluoride release system or fillers. The adhesive is characterized by high shrinkage. Another one part adhesive that is available is comprised predominantly of an acetone solvent and a BPDM adhesion promoter. The adhesive also contains no fluoride release system or fillers. It provides only a medium bond strength and also is characterized by high shrinkage.
U.S. Pat. No. 5,348,988 discloses a dentin bonding system which utilizes unsaturated carboxy esters as bonding agents produced by the reaction of unsaturated alcohols with cyclic acid dianhydrides, with BPDM as part of the dentin bonding system. The system also comprises a dentin conditioner which is the reaction product of a cyclic acid anhydride with an ethylenically unsaturated alcohol, and a two-part dentin primer, the first part of which comprises the reaction product of an N-arylglycine with glycidyl methacrylate. The second part of the two-part dentin primer is selected from products such as BPDM. The patent also discloses the use of a solvent such as acetone. The composition is applied in solution to an area to which a bond is desired, and the bond is completed by use of a self-curing initiator or a light cure system. Other materials such as camphoquinone are disclosed as being useful. Premixed or one part adhesives that are water based are also available. The water based adhesives, while more stable than the acetone or alcohol based adhesives, require a predrying of the tooth area on which the adhesive is being applied, because moisture on the surface of the tooth can change the properties of the adhesive. Water based adhesives have also been found to be less strong.
The adhesives of the prior art that are discussed above possess a common problem of the evaporation of the product. This is particularly a problem with the one part organic solvent based adhesives, but is also true of water based and other solvent based adhesives. Such adhesives possess the desired composition upon the first opening of the bottle or container in which they are delivered, but before a substantial portion of the adhesive is used, evaporation of a portion of the solvent and other high volatility components occurs, leaving the balance of the adhesive with increased composition of the other components and increased viscosity. This change in concentrations adversely affects the application of the adhesive and the quality and resulting performance of the bond.
In addition, the use of bulk delivery systems for packaging one part adhesives has had several undesirable features. One such feature has been the multiple number of times that the container must be opened, handled and resealed. Each time the container is opened and handled, a potential exists for contaminating the entire contents of the container. For example, if the container is sealed with a cap which must be removed to dispense the adhesive, the cap may become contaminated if placed on a dental operatory tray or any other resting place while the contents of the container are being dispensed. When the cap is reset on the container to reseal it, the contents of the container may become contaminated. In addition, the dentist or dental assistant whose hands may have had contact with the mouth of a patient being treated may contaminate the cap while holding it or may contaminate the opening in the container through which the contents are dispensed.
Another undesirable feature of the bulk delivery system is that the dentist or dental assistant is required, each time the adhesive system is used, to accurately dispense the correct amount of adhesive from the container. If an insufficient amount is dispensed, the steps involved in dispensing the adhesive must be repeated. If an excessive amount of adhesive is dispensed, the excessive adhesive is wasted.
A further undesirable feature of the prior art systems is that they increase the opportunity for evaporation of portions of the adhesive. This can occur when the container holding the adhesive is unsealed. In the unsealed state, the adhesive is exposed to the atmosphere of the dental office. This can cause the portions of the adhesive to evaporate which will affect the performance of that portion of adhesive remaining in the container when it is later used. If the container remains unsealed for an extended period of time, an amount of the adhesive base sufficient to affect the performance of the adhesive may evaporate.
As a result of the above, there has been a demand for some time by dentists for adhesives that are more convenient, easier to use, and less susceptible to degradation prior to their use and for a delivery system that will preserve the purity of the adhesive, deliver a pre-measured amount of adhesive and reduce the likelihood of evaporation of the adhesive contents. Notwithstanding this demand, an effective combination of adhesive and container for delivery to the dentist has not been found. Accordingly, a need remains for an adhesive delivery system, particularly for use in applying dental restorations.